Pneumatic tires for high speed applications experience a high degree of flexure in the crown area of the tire as the tire enters and leaves the area of the footprint. This problem is particularly exacerbated on aircraft tires wherein the tires can reach speed of over 200 mph at takeoff and landing.
When a tire spins at very high speeds the crown area tends to grow in dimension due to the high angular accelerations and velocity, tending to pull the tread area radially outwardly. Counteracting these forces is the load of the vehicle which is only supported in the small area of the tire known as the footprint area.
Current tire design drivers are an aircraft tire capable of high speed, high load and with reduced weight. It is known in the prior art to use zigzag belt layers in aircraft tires, such as disclosed in the Watanabe U.S. Pat. No. 5,427,167. Zigzag belt layers have the advantage of eliminating cut belt edges at the outer lateral edge of the belt package. The inherent flexibility of the zigzag belt layers also help improve cornering forces. However, a tire designed with zigzag belt layers may result in too many layers at the belt edges which may reduce durability. Further, there is generally a tradeoff between load capacity and weight. Thus an improved aircraft tire is needed, which is capable of meeting high speed, high load and with reduced weight.
Definitions
“Carcass” means the tire structure apart from the belt structure, tread, undertread, and sidewall rubber over the plies, but including the beads.
“Circumferential” means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction.
“Cord” means one of the reinforcement strands of which the plies in the tire are comprised.
“Equatorial plane (EP)” means the plane perpendicular to the tire's axis of rotation and passing through the center of its tread.
“Modulus of elasticity” of a cord at a given strain or stress means the extension secant modulus calculated at the given strain or stress. A high elastic modulus means a secant elastic modulus over 1000 cN/tex and a low elastic modulus means a secant modulus under 600 cN/tex.
“Ply” means a continuous layer of rubber-coated parallel cords.
“Radial” and “radially” mean directions radially toward or away from the axis of rotation of the tire.
“Radial-ply tire” means a belted or circumferentially-restricted pneumatic tire in which the ply cords which extend from bead to bead are laid at cord angles between 65° and 90° with respect to the equatorial plane of the tire.
“Section width” is the distance between a tire's sidewalls measured at the widest part of the tire when inflated to rated pressure and not under load.
“Tangent modulus of elasticity” of a cord at a given strain or stress means the extension tangent modulus of the cord. At a given stress or strain, the tangent modulus of elasticity is the value of the slope of the tangent to the stress strain curve, and can be determined from ASTM E111-04, entitled “Standard Test Method for Young's Modulus, Tangent Modulus, and Chord Modulus.”
“Zigzag belt reinforcing structure” means at least two layers of cords or a ribbon of parallel cords having 1 to 20 cords in each ribbon and laid up in an alternating pattern extending at an angle between 5° and 30° between lateral edges of the belt layers.